Vibration isolation systems typically include a platform and a plurality of isolators often one in each corner of the platform. An isolator may include a piston on a diaphragm supporting the platform. A first (top) pressurized air chamber supports the diaphragm and a second (bottom) pressurized air chamber supplies air to the first chamber and acts as a reservoir.
In some designs, stiff and soft modes of isolation are possible. Reasons to control the stiffness of the isolator include responding to loads or changes in loads on the platform. When the isolation platform is used to isolate a machine (such as a shaker) from the floor of a building, it can be desirable to adjust the stiffness of the system in real time based on the operation cycle of the machine. U.S. Pat. No. 6,123,312, for example, incorporated herein by this reference, shows a pressure regulator regulating the pressure in the second chamber based on the load on the platform. The second chamber is connected to the first chamber via an isolation controller which controls the gas flow rate from the second chamber to the first chamber. A control signal controls the isolation controller and thus the stiffness of the isolator.
In another design, a valve allows air to flow from the second chamber to the first chamber via either high or low resistance coils in order to control the stiffness of the isolator.
Other relevant prior art may include U.S. Pat. Nos. 4,796,873; 7,114,710; 4,531,699; 4,735,296; 5,061,541; 5,348,266 and 5,962,104, all of which are incorporated herein by this reference.